By moving supports A and C along respective tracks (3) and (4), the free end B of robot arm (2), with gripper (5), is caused to move along a path P, the locus of which may be varied by varying the movements of the supports A and C. Motors (6) and (7) are not carried on the robot arm (2), but are secured to the frame (10) of the device (1). The robot arm (2) may thus have very low mass, resulting in very high performance in terms of speed and efficiency. The path P may comprise a NURB curve, and the time-distance function of motion of end B of arm (2) along path P may comprise a polynomial function having first and second derivative (velocity and acceleration) continuous curves.